Vacuum furnace with elevator oil quench

ABSTRACT

A high-vacuum electric furnace for heat treating metallic articles in an evacuated heating chamber and including an elevator to which the articles are transferred after the heattreating cycle for transferring the articles to a quench zone for the quick quenching thereof, the quenching zone communicating with the housing in which the heating zone is located and being maintained under vacuum during the quenching operation.

United States Patent [54] VAClJUM FURNACE WITH ELEVATOR OIL PrimaryExaminerFrank T. Yost Attorney-Sa1ter & Michaelson ABSTRACT: Ahigh-vacuum electric furnace for heat treating 2: 3 H 12 D metallicarticles in an evacuated heating chamber and includ- 8 rawmg ing anelevator to which the-articles are transferred after the [52] U.S.Cl266/4 A, heat-treating cycle for transferring the articles to a quench148/153 zone for the quick quenching thereof, the quenching zone [51]Int. Cl C21d 1/66 communicating with the housing in which the heatingzone is [50] Field of'Search 266/4, 4 A, located and being maintainedunder vacuum during the 4 B, 4 E, 15; 148/143, 144, 153quenching-operation.

| A9 l 1 l l 52 /741 I I I v 1 1 l l 1 PATENTEUAUGITISII 3,599,946

sum 1 or 6 INVENTORS HERBERT W. WESTEREN WILLIAM H. K MBALL VINCENT S00T0 W LACE S. VANDERFORD, JR.

ATTORNEYS PATENTED AUG I 7 Ian SHEET 2 [IF 6 %.w\ why NNX wx Q $9M w N9v wm m .l 1 Q NW 39X N H J 9% 9% Q N mm I I u n I I n I n u. M H km QHERBERT w. WILLIAM H. K

ATTORNEYS PATENTEU AUBI H971 SHEET 3 OF 6 A II I M- TEL INVENTORS W.WESTEREN H. K ALL 800 HERBERT S. ERFORD, JR.

VA NQ FIG.4

ATTORNEYS PATENHED we: 7 IQYI SHEET 4 UF 6 INVENTORS WESTEREN FIGGHERBERT WILLIAM VINCENT ATTORNEYS PATENTED W 71971 SHEEI 5 [IF 6 VINCENTS COT WlLACE S. VANDERFORD,JR. M 3" ATTORNEYS PATENTED AUG] 7 IBYI SHEET6 OF 6 INVENTORS ATTORNEYS VACUUM FURNACE WITH ELEVATOR QUENCHBACKGROUND OF THE INVENTION The present invention relates to furnacesfor heat-treating metallic articles.

In the heat treatment of metallic articles, such as carbon and stainlesssteels and the like, it is critical in certain conditions of use thereofthat the surfaces of the article be maintained free from contaminationthat results from oxidation and/or decarbonization. The techniqueemployed for heattreating articles heretofore has normally consisted ofheattreating in a subatmospheric environment and then moving thearticles to a cooling zone through which a cooling atmosphere' wascirculated. Although cooling in an atmosphere was effective in certainheat-treating procedures, proper hardening of certain materials couldnot be obtained by atmosphere cooling since this procedure required arelatively long quench cycle and the desired metallurgical structurenecessitated a quick quench.

As described in copending application Ser. No. 422,617, filed Dec. 31,1964 and entitled HIGH VACUUM ELECTRIC FURNACE, the technique ofquenching the heat-treated article in a liquid, such as oil, providedfor dumping of the heattreated articles from a transfer zone into an oilquench tank located directly below the transfer zone. Although the priortechniques of quenching in oil under vacuum as disclosed in theabove-noted pending application resulted in the desired hardening andbright surface, the dumping process was usable only with certain smallarticles and could not be employed for machined parts that were subjectto damage by dumping into a quench tank.

SUMMARY OF THE INVENTION The present invention relates to a method andapparatus for vacuum heat-treating metallic articles and provides forextracting of the heat-treated articles from a heating zone after theheating cycle for movement to a transfer zone at which theyare locatedon an elevator. With the heat-treated parts mounted on the elevator inpositive relation, the elevator is then quickly moved downwardly fromthe transfer zone to a quench zone at which the quenching operation iscarried out in a liquid, such as oil. Since the metallic articles areretained in a fixed position on the elevator as they are movedto thequench zone, a great variety of relatively large articles can be oilquenched without risk of mechanical damage, which would normally occurin a dump quench operation.

In carrying out the invention, a unique transfer mechanism is employedfor retracting a work cart, on which the articles are contained, fromthe heating zone to the elevator. The

retracting mechanism which, in effect, tethers the work cart, cooperateswith the means for operating the elevator so that the work cart isretained in a fixed position on the elevator as it is moved therewithfrom the transfer zone to the quench zone during the quenchingoperation. Since it is necessary to quickly move the articles into thequench liquid, means are further provided for controlling the rate ofdescent of the elevator so that as it approaches the surface of thequench liquid, it is caused to rapidly descend therethrough. Themovement of the elevator is then controlled so that after it movessubstantially through the quench liquid, it is caused to move to a lowerposition in the quench tank without shock, and then after the quenchingoperation is completed, the elevator is moved upwardly to the transferzone for removalof the articles from the fumace.

Quenching of the heat-treated articles is carriedout by the elevatormechanism of the present invention by rapid transfer of the articlesfrom the transfer zone to the quench tank, thus ensuring that rapidquenching of the articles is achieved. Since the articles arecontinuously exposed to a subatmospheric environment prior tointroduction thereof into the quench liquid contained in the quenchtank, surface contamination ofthe articles is prevented, and anunusually clean and bright surface on the articles is obtained.

The vacuum furnace as embodied herein is essentially concerned with theheat treatment of articles under vacuum and transfer of the heat-treatedarticles to a quench tank without removal of the articles from withinthe vacuum vessel. However, in order to obtain the results as set forthhereinafter, various constructional features, including a uniquetransfer elevator, are embodied in the vacuum furnace that provide forthe efficient operation thereof, and such features and constructions aredescribed hereinafter.

Accordingly, it is an object of the invention to provide a high-vacuumfurnace for heat-treating and quenching metallic articles in such amanner as to prevent contamination of the surfaces thereof.

Another object of the invention is to provide a high-vacuum electricfurnace in which articles to be heat-treated are moved within thefurnace by remotely controlled means for automatic transfer from theheating zone to a transfer zone and thereafter into a quenching zone.

Still another object is to provide a control mechanism for withdrawing awork cart on which the articles are located from the heating zone to atransfer zone, the control mechanism including a device for locking thework cart on the elevator when the elevator is moved into the quenchzone for the quenching for the quenching of the articles therein.

Still another object is to provide means for controlling the verticalmovement of an elevator such that the articles are rapidly moved to thequenching medium for the quick quenching thereof.

Still another object is to provide a unique cooling system for thehousing of the furnace which includes means for continuously circulatinga cooling fluid in circular relation around an inner shell of thehousing.

Other objects, features and advantages of the invention will becomeapparent as the description thereof proceeds when considered inconnection with the accompanying illustrative drawings.

DESCRIPTION OF THE DRAWINGS In the drawings which illustrate .the bestmode presently contemplated for carrying out the present invention:

FIG. 1 is a vertical sectional view of the high-vacuum electrio fumaceembodied in the present invention;

FIG. 2 is a horizontal sectional view of the vacuum furnace illustratedin FIG. 1;

FIG. 3 is a sectional view taken along lines 3-3 in FIG. 1;

FIG. 3a is a sectional view taken along lines 3a-3a in FIG. 1;

FIG. 4 is a fragmentary sectional view of a portion of the furnaceshowing the control device that is employed for retracting the work cartfrom the heating zone to the transfer zone;

FIG. 5 is a perspective view of an end of the work cart and showing theinterconnection thereof to a tape that is operable to retract the cartfrom the heating zone;

FIG. 6 is a fragmentary side elevational view of the work cart showingthe heat shields that are associated therewith;

FIG. 7 is a partial end view, with portions shown in section, of theheat shields that are illustrated in FIG. 6;

FIG. 8 is a perspective view showing the elevator lift mechanism and theretract mechanism for the work cart that retains the cart on theelevator in locked relation;

FIG. 9 is a side elevational view of the furnace showing the exteriorpiping for the cooling system;

FIG. 10 is an end elevational view of the furnace housing with portionsbroken away showing the circulation of the cooling fluid in the coolingspace as defined between the inner and DESCRIPTION OF THE INVENTIONReferring now to, the drawings and more particularly to FIGS. 1, 2 and3, the vacuum furnace embodied in the present invention is illustratedand is generally indicated at 10. Since the vacuum furnace is operatedat a predetermined vacuum, any suitable vacuum equipment may beconnected thereto for evacuating the interior thereof as required, andas illustrated in FIG. 3 a vacuum pipe 11 is fixed in the furnacehousing and communicates with a vacuum pump (not shown). As illustratedin FIGS. 13, the vacuum furnace 10 includes a housing generallyindicated at 12 that is defined by an outer shell 14, an inner shell 16to which an end wall 18 is fixed and on which a door 20 is removablymounted. The removable door 20 is slidable on suitable tracks (notshown) and is mova ble transverse to the longitudinal axis of thefurnace to expose the furnace interior when a workload is introducedtherein or removed therefrom after a heat-treating operation.

As will be described hereinafter, the outer shell 14 of the housing 12that surrounds the inner shell 16 is substantially rectangular in crosssection as compared to the circular cross section of the inner shell 16,the spacing between the inner and outer shells defining a cooling spacethrough which a cooling fluid, such as water, is continuously circulatedfor maintaining the temperature of the housing walls at a prescribedlevel. As further illustrated in FIG. 1, both the door 20 and end wall18 are jacketed to receive a cooling fluid therein for maintaining theseparts at the prescribed temperature level.

The furnace 10 is of such size as to require a substantial supporttherefor, and, accordingly, spaced transverse beams indicatcd at 22, 24and 26 and longitudinal beams. 27 and 29 are positioned beneath theouter shell 14 for supporting the furnace thereon. The beams 22, 24, 26,27 and 29 may be fixed in a flooring or the like or located in anysuitable manner. As will be further described, the housing 12 includes aquench zone into which the heat-treated articles are moved during thequenching operation. Since the quench zone must be located remote fromthe heating zone and if the housing 12 is mounted directly on aflooring, a suitable cavity must be formed in the flooring for receivingthe quench tank as illustrated in FIG. 1 and as will be furtherdescribed.

Located within the housing 12 and adjacent to the door 20 is a transferzone 28, while located adjacent to the transfer zone 28 is a heatingzone 30. The articles to be heat-treated are moved into the transferzone 28 prior to introduction thereof into the heating zone 30, andfollowing the heating cycle the articles are returned to the transferzone for movement therefrom into a quench zone 31 that is locateddirectly below the transfer zone 28. As shown more clearly in FIG. 1,the heating zone 30 includes an enclosed heating chamber 32 that isdefined by a casing formed of flexible insulating graphite material. Thegraphite insulating material is arranged in layers and, as shown inFIGS. 1, 2 and 3 includes a top wall 34, a bottom wall 36, sidewalls 37and 38, a rear wall 39, and a front wall 40 in which an opening 42 isformed. Located within the heating chamber 32 are a plurality of tubularresistance-heating elements 44 that are disposed in spaced relation andare interconnected at the ends thereof to suitable terminals 46. Asdescribed in copending application Ser. No. 724,716, filed Apr. 29,1968, and entitled ELECTRIC FUR- NACE AND TUBULAR HEATING ELEMENT FORUSE THEREWlTI-I, the tubular heating elements 44 are formed of aflexible woven graphite material and are arranged in tubular formation,the terminals 46 of the tubular heating elements being fixed to bus bars48 that extend exteriorly of the furnace housing 16 through connections(not shown) for communication with a suitable source of current. Upperhanger brackets 50 and lower support brackets 52 are fixed in theheating zone 30 for mounting the insulating walls of the heating chamber32 in place.

Located within the heating zone 30 and fixed to the inner shell 16 ofthe housing 12 are a plurality of spaced roller supports 54 on whichrollers 56 are mounted. The rollers 56 are rotatable in suitablebearings that are positioned in the supports 54; and, as will bedescribed, the rollers 56 are provided for receiving a work pedestal orcart that is moved into the furnace housing during the heating cycle. Inorder to fix the supports 54 within the heating zone, a plurality ofplates 58 are joined to the shell 16 and receive the supports 54 insecure relation thereon.

After the heating cycle has been completed and the workload removed fromthe heating chamber 32, it is desirable to seal the heating chamber soas to effectively retain the heat therein during the cooling andquenching cycles. In order to seal the heating chamber 32, a door 60 ispivotally mounted on the front wall 40 of the chamber and, asillustrated in FIG. 1, the door 60 also includes a plurality ofinsulating layers that preferably are formed of a graphite material. Inorder to automatically control the movement of the door 60 exteriorly ofthe furnace, a metal tape 62 is connected to the door 60 and extendsover a pulley 64 and though a tube 66 at the bottommost portion of whichthe pulley 64 is mounted. The tube 66 extends through a vacuum seal 68that spans the inner and outer shells of the housing, and the tape 62that extends through the seal 68 is operatingly connected to a pistonrod 70 of a control cylinder that is preferably operated exteriorly. Aswill be described when the workload is moved out of the heating chamber32 following the heating cycle, the door 60 is automatically closed bythe control cylinder to effectively retain the heat within the heatingchamber 32.

As previously mentioned, the door 20 is movable to an open positionduring unloading or loading of the articles to be heattreated. With thedoor 20 in an open position, a basket is placed on a work pedestal orcart generally indicated at 72, which, as shown in FIG. 1, is located inthe transfer zone 28 on an elevator generally indicated at 74. As willbe described hereinafter, the elevator 74 is adapted to move the workcart 72 and articles thereon to the quench zone 31 below the transferzone 28, but, for the purpose of moving the work cart and the articlesthereon to the heating zone 30, the elevator 74 is disposed in theuppermost position thereof, as illustrated in full lines in FIG. 1.

As shown in FIG. 2, the cart 72 is essentially a three-sidedconstruction and is defined by spaced channel-shaped side members 78 and80 and an end member 82. As illustrated in FIG. 7, the side members 78and 80 have a reversely formed channel configuration that receive therollers 56 therein, the rollers 56 thus defining tracks over which thecart 72 is moved between the transfer zone 28 and the heating zone 30.Interconnecting the side members 78 and 80 are a plurality of spacedbars 84 that are preferably formed of a molybdenum material, the outerends of the molybdenum bars 84 being received in convenient verticalslots formed in the sides 78 and 80 and being locked in place therein byouter flanges, as indicated at 86 and 88 in FIGS. 2 and 6.

Since the width of the cart 72 is greater than the width of the heatingchamber 32 as defined by the walls 37 and 38, the side members 78 and 80extend outwardly of the heating chamber walls 37 and 38. In order toaccommodate the bars 84 that support the work basket and load thereon,the walls 37 and 38 are formed with slots, as indicated at 90 and 92 inFIG.

3. Referring now to FIGS. 6 and 7, a portion of the work cart isillustrated as it is located in the heating chamber 32, the bars 84extending through the slots 90 and 92 formed in the walls 37 and 38respectively. Since considerable heat can escape through the slots 90and 92 during the heating cycle, a heat shield assembly is provided thateffectively shields the heating chamber 32 for retaining the heattherein. As shown in FIGS. 6 and 7, a plurality of outer heat shields 94are joined to the side members 78 and 80 through brackets 96 that may bewelded to the upper surfaces of the side members, each of the outershields 94 being spaced between the bars 84. An end plate 97 is joinedto the endmost of the outer shields 94 and defines an end barrier. Fixedto the outer shields 94 and spaced therefrom for location within theslots 90 and 92 are spaced inner shields 98 and 100, the outer shields98 and 100 being located between spacer tubes 102 and 104 and beingfixed in position by a bolt 106 on which a nut 108 is received. It isseen that the outer shield 94 and the inner shields 98 and 100effectively prevent heat radiation through the slots 90 and 92 when thecart 72 is located within the heating chamber 32 during the heatingcycle.

In carrying out the heat-treating of the metallic articles within thefurnace 10, the present invention provides for quick quenching of theheat-treated articles in the quenching zone 31 after completion of theheat-treating cycle. As shown more clearly in FIG. 1, the quenching zone31 is defined by a quench tank 110 that is located within a jacket 112through which a cooling fluid is continuously circulated. The quenchtank 1 is disposed directly below the transfer zone 28, and it iscontemplated that in the installation of the furnace 10, the quench tank110 will be located below floor level so as to properly accommodate thequench tank with respect to the transfer zone 28 and heating zone 30. Inthis connection the height of the quench tank 110 is arranged such thatthe quench medium, which is preferably oil, is disposed at a sufficientlevel below the transfer zone 28. Thus, during the quenching cycle, anyvaporization of the oil will be effectively trapped at the upper levelof the quench tank, and contamination of the transfer zone and heatingchamberwill be effectively prevented. In order to condense any vaporizedoil molecules and to prevent contamination of the transfer zone andheating zone, the upper level of the quench tank isenveloped by thejacket 112 for circulation of the cooling fluid therebetween, whereinthe upper portion of the quench zone is effectively cooled. Purifyingthe quench medium and aiding in the cooling action is also produced byagitation of the quench medium by opposed impellers 114 and '1 16 thatare located within the quench tank adjacent to the sidewalls thereof. Asshown in FIG. 3, the impeller 114 is driven by a motor 118 supportedfrom the housing support beam 27 located exteriorly of the quench tank110, while the impeller 116 is driven by a motor 120 supported from thebeam 29. Suitable seals 119 and 121 are provided for receiving theimpeller shafts that are interconnected to the motors 118 and 120.

As previously described, the elevator 74 is provided for moving the workcan 72 and the articles as contained in a basket thereon into the quenchzone 76 for the quick quenching of the articles following the heatingcycle. As shown in FIGS. 1 and 2, the elevator 74 is defined by a framethat includes spaced front frame members 122 and 124 that areinterconnected by bracing elements 126 and 128, side frame members 130and 132, and a rear frame member 134. Joined to the frame members 124and 134 are elongated supports 136 and 138 on which a plurality ofvertical roller brackets 140 are mounted for supporting rollers 142thereon. Fixed within the transfer zone 28 by upper brackets 143 and 145and extending downwardly within the quench tank 110 are spacedchannel-shaped tracks 144 and 146. Followers 148 and 150 are receivedwithin the tracks 144 and 146 and are operatively joined to the framemembers 130 and 132 of the elevator frame. Thus, movement of theelevator will be substantially vertical as the followers 148 and 150 areguided within the tracks 144 and 146.

In order to vertically move the elevator 74 with the work cart 72mounted thereon, a hydraulic lift is employed and, as shown in FIG. 1,includes a cylinder 152 that is mounted within the quench tank 110 on asupport bracket 154. A first ram 156 is telescopically received withinthe cylinder 152, the first ram 156 receiving a second ram 158 intelescoping relation therein. Joined to the topmost ram 188 isacrosshead 160 on which spaced sprocket wheels 162 and 164 are fixed.Chains 166 and 167 are secured at the lower end of the cylinder at 168and 169 respectively, and extend around the sprocket wheels 162 and 164are joined to links 170 and 171 (FIG. 5) fixed to the elevator 74 on thefront frame member 122. It is seen that upon actuation of the hydrauliclift, the rams 156 and 158 will be vertically moved to operate thechains 166 and 167 for moving the elevator 74 in a correspondingdirection. Because the lift moves vertically as the pulleys are rotatedon the crosshead 160 a 2:1 mechanical advantage for movement of theelevator is obtained. Since the guide followers 148 and are disposed formovement within the tracks 144 and 146, the elevator 74 must move in aprescribed vertical direction between the transfer zone 28 and thequench zone 76 upon operation of the hydraulic lift. As will bedescribed hereinafter in the operation of the furnace, the fluid mediumfor operating the hydraulic lift is the quench liquid as contained inthe quench tank 110. By utilizing the quench liquid for the liftcylinder, contamination of the quench zone by a hydraulic fluid ascontained in an exterior system is avoided. It is for this reason thatthe lift cylinder 152 is mounted within the quench tank 110 asillustrated in FIG. 1.

When the work cart 72 is introduced into the furnace at the transferzone 28 and thereafter moved into the heating zone 30, it is necessaryto provide for automatically retracting the work cart onto the elevator74 so that the elevator may then be lowered into the quench zone 76 forthe quick quenching of the heat-treated articles. As illustrated inFIGS. 5 and 8, a tethering and locking device that is automaticallyoperable externally of the furnace is provided and is adapted to beinterconnected to the cart 72 for retracting it from the heating zone30. The tethering and retracting device includes an elongated metal tape172 that is wound on a reel 174, the reel 174 being mounted on a shaft176 that is journaled for rotation in bearings 178 and 180 that areconveniently mounted on a bracket 181 located within the transfer zone28. As shown in FIG. 4, the shaft 176 extends outwardly of the furnacehousing through a seal 182 and has a pinion 183 mounted on the outermostend thereof that is engageable by a rack 184. The rack 184 is connectedto a piston rod 185 that is reciprocally moved by an automatic controldevice for effecting rotation of the shaft 176 and movement of the tape172 as required.

The tape 172 as it extends from the reel 174 is received on a movableidler 182 and extends over a fixed idler 183 that is journaled betweenspaced plates 184 and 186 that are fixed to the frame 122 of theelevator. As shown in FIG. 4, the idler 182 is interconnected to thecrosshead 160 through a bracket 187, the idler 182 moving with thecrosshead 160 and relative to the elevator. Thus as the lift descendsthe elevator that is connected to the chains 166, 167 is lowered at amore rapid rate. The tape 172 is maintained in tensioned relation duringthis movement since it will be taken up by the vertical position of theidler 182. In order to tether and lock the work cart 72 on the elevator74, the end member 82 of the cart is formed with holes through which thelegs 188 of a U-shaped rod 190 extend (FIG. 5), the legs 188 also beingreceived in suitable openings formed in brackets 192 and 194 that aresecured to the end member 82. The free end of the tape 172 is lockedaround a pin 196, shown in FIG. 8, and the pin 196 is located betweenthe legs 188 of the rod 190 and the brackets 192, 194. It is seen thatas the tape 172 is retracted onto the reel 174, the pin 196 will engagethe brackets 192 and 194 and will cause the cart 72 to follow themovement of the tape 172. When the work cart reaches the fully retractedposition in the transfer zone 28, the pin 196 is received at stop pointsindicated at 198 and 200 on the plates 184 and 186 and the cart is thenlocated in the locked positionon the elevator 74 and will be retainedtherein by the fully wound tape on the reel 174. It is seen that in thefully retracted position and with elevator 74 located in the transferzone 28, the idler 182 is at its uppermost position. As the hydrauliclift lowers the work cart 72 within thequench zone 31, the idler 182will move downwardly with the crosshead 160, tensioning the tape 172during the downward travel of the elevator, thereby retaining the workcart 72 in its fully locked and. tethered position.

Thus, when the work cart reaches the quench zone 31 on the elevator 74,it will be locked in position by the tape 172 and the articles ascontained thereon will be suitably positioned on the cart during thequenching operation. It is further seen that movement of the cart 72over the elevator and through the door opening can be accomplishedfollowing the complete heat-treating cycle by lifting the rod 190 fromits position in the member 82. Since the cart is then essentiallyreleased from the tape 172 it may be pulled over the elevator plates184, 186 and reel 174 and through the door opening.

During the quenching cycle and upon movement of the elevator 74 into thequench zone 31, it is essential that the elevator and articles thereonbe moved rapidly into the quench liquid. However the elevator cannotfall too rapidly from the upper position in the transfer zone 28 orsplashing will occur that will contaminate the furnace interior. As willbe described in the operation of the apparatus a special control systemis provided for slowly dropping the elevator to just above the quenchliquid and then rapidly moving the elevator into the quench liquid. Thiscontrol system includes an actuating arm 202 that is mounted on theelevator 74 and extends thereabove, the actuating arm 202 being adaptedto engage an operating element of a control valve for effecting thecontrol of the system that provides the intended movement of theelevator.

Prior to the instant invention the housings of vacuum furnaces haveusually been constructed of a stainless steel material, which, in largeinstallations, is relatively costly. In the present invention the use ofstainless steel in the furnace housing is avoided by forming the housinginner shell 16 of a mild steel and then applying a thin Teflon coatingto the outer surface of the inner shell 16. The Teflon coating not onlyprevents corrosion of the inner shell which is normally subjected towater circulation therearound but effectively reduces the overall costof the furnace construction. Protection of the vacuum vessel walls asrepresented by the inner shell 16 is also contemplated by chemicallytreating the circulating cooling liquid. This would effectively resistcorrosion. Further, the use of a heat exchanger in the cooling systemwould reduce the corrosive activity of the cooling fluid on the innershell. If desired, the outer jacket 14 may also be formed of a mildsteel.

It has been the usual practice in cold wall vessels of the general typeembodied in the present invention to enclose a cylindrical inner shellin a cylindrical outer shell and circulate a cooling mediumtherebetween. However, circulating the cooling medium between thecylindrical shells heretofore has been relatively inefficient, since thetemperature of the inner shell could not be easily controlled because ofthe poor circulation of the cooling fluid. In order to adequately coolall of the surfaces of the furnace as embodied in the present invention,a large flow of cooling liquid is required. This is accomplished byenclosing the inner shell 16 with the outer shell 14 that has asubstantially rectangular configuration in vertical cross section asillustrated in FIG. 10. The outer shell 14 is open at the top to furtherprovide for effective cooling of the circulating fluid, the fluid beingdirected in a circulating flow around the inner shell !16. For thispurpose, a plurality of jets 206 are located along the length of theouter shell 14 and introduce the cooling fluid under pressure into thecooling space between the inner and outer shells 14 and 16. As shown inFIGS. 9 and 10, the cooling system includes a pump 208 that supplies thejets 206 with the cooling fluid, such as water, and receives acontinuous flow of the cooling fluid through a pipe 210 thatcommunicates with the outer shell adjacent to the upper end thereof. Asseen in FIG. 10, the jets 206 are located substantially tangential tothe inner shell 16; and thus, upon injecting of the cooling fluid intothe cooling space, a circulating action of the cooling fluid isproduced, as indicated by the arrows in FIG. 10. It is also seen thatsuction of the water through the pipe 210 by the pump 208 furtherinduces the circulating action of the cooling fluid. In the event thatthe temperature of the cooling fluid in the cooling space exceeds aprescribed level, fluid such as water can be added through a supply pipe212, as indicated in FIG. 9, and an inlet pipe 214 that communicateswith the cooling space adjacent to the upper end thereof. In the eventthat excess cooling water is introduced into the cooling space, a drain216 is provided for draining the excess as required.

As shown in FIG. 12, the cooling system also provides for introducingthe cooling fluid to the various areas of the furnace that requirecooling. Thus, a pipe 218 supplies the cooling fluid to the coolingspace between the quench tank 110 and the jacket 112. Pipe 220 providesthe necessary cooling fluid for the end wall 18. The bus bars 48 arewater cooled, and convenient flexible tubing 222 is connected to the busbars 48 for conducting the cooling fluid thereto. Additional pipes 224and 226 connected to the supply pipe 212 are also provided forconducting the cooling fluid to the jacketed space in the door 20. Aflexible hose 227 that is interconnected to the pipes 224 and 226enables the door to be shifted laterally during loading or unloading ofthe furnace.

As mentioned above, the inner shell 16 is formed of mild steel and has athin Teflon coating applied thereto. In order to visually inspect theinner shell 16, the outer shell 14 has a plurality of inspection ports219 located in the sidewalls thereof, as indicated in dotted lines inFIG. 1. As shown in FIG. 3a, an annular flange 221 surrounds each of theports 219 and receives a cover plate 223 thereagainst in sealingrelation. Sealing dogs 225 are bolted to the flange 221 and engage thecover plate 223 for locking it in sealing engagement against the flange221. It is seen that after the cooling fluid is removed from the coolingspace between the shells, the cover plates 223 may be removed to uncoverthe ports 219, whereupon the inner shell 16 may then be visuallyinspected.

OPERATION In operation of the furnace 10 as embodied herein, a workloadis first placed in a convenient basket or receptacle, and the workloadas contained in the basket is placed on a transfer table (not shown) asit is located outside the furnace. With the door 20 open, the transfertable is rolled adjacent thereto, and the basket and workload thereonare moved therefrom onto the cart 72 as it is located on the elevator 74in the transfer zone 28. The work cart 72 is then moved into the heatingzone 30, wherein the work basket and the articles to be heat-treated ascontained therein are located within the heating chamber 32. The door 20is closed and sealed and the furnace evacuated for the heating cycle.Since the transfer zone 28, heating zone 30 and quench zone 76 are allin open communication, all of these zones are evacuated by the vacuumpump equipment during the heat-treating cycle. It is understood thatwhen the work cart 72 is moved into the heating zone 30 as illustratedin FIG. 2, the tape 172 has been interconnected therewith, and isunwound from the reel 174 as illustrated in FIG. 2. The cycle ofoperation is then automatic as will now be described. After the heatingcycle has been completed, the pump valve interconnecting the furnace andvacuum pump is closed. The furnace is then backfllled with nitrogen to adesired subatmospheric pressure, preferably about 12 in. hg. and theoil-circulating pumps 114, 116 are started. When the transfer chamber 28reaches the desired backfill pressure, the control cylinder for the door60 is actuated to cause the door to be moved to the open position, asillustrated in FIG. 1. The cylinder operating the rack 184 is nextactuated and the reel 174 is rotated by the pinion 183 to retract thetape 172, thereby withdrawing the work cart 72 and basket thereon intothe transfer zone 28. As the cart 72 is withdrawn from the heating zone,the side members 78 and 80 are received on the rollers 142 of theelevator 74. When the tape 172 is fully retracted, the work cart 72 isdisposed in tethered and locked position on the elevator 74. The door 60is now returned to the closed position and the apparatus is ready forthe quenching cycle.

Referring now to FIG. 11, a diagrammatic illustration of the system forcontrolling the operation of the hydraulic lift is illustrated, andmovement of the elevator during the quenching cycle will now bedescribed. When the work cart reaches the transfer zone and is locatedon the elevator, a solenoid operated three-way valve 228 is energized tolocate the actuating portion of the lift cylinder 152 in communicationwith the interior of the quench zone 31 by way of lines 230, 232, 234and'236. As the hydraulic fluid bleeds out of the cylinder 9 152 intothe quench tank 110, the elevator slowly descends. As previouslymentioned, it is desirable to move the heattreated articles through thesurface of the quench liquid very rapidly so as to effect a quickquenching thereof, and thereby prevent vaporization of the quenchingmedium, In order to a accomplish this purpose, the operating arm 202moves into engagement with the operating element of the control valve238. The control valve 238 is thenplaced in communication with the line234 by way of line 240. The operating fluid that is bleeding from thecylinder 152 into the quench tank 110 by way of line 236 is now furtherexhausted into the quench tank through the line 240, valve 238 and ableed valve 242. The elevator then quickly descends through the surfaceof the quench medium and drops substantially into the quench tank. Asthe operating arm 202 passes over the actuating element of the valve238, this valve is then once more closed to prevent the operating fluidfrom exhausting into the quench tank 76. The elevator then slowlydescends to the bottom of the quench tank without undue shock as theelevator reaches the bottom of the tracks 144 and 146.

After a predetermined period for quenching of the articles within thequench zone, the three-way solenoid valve 228 is automatically activatedto place the exhaust of a pump 246, mechanically interconnected to anair-operated motor 244, into communication with the line 232. Theoperating fluid is now pumped from the quench tank into the cylinder 152by way of line 236, control valve 250, line 252, exhaust line 254, andline 232. Since the pump 246 draws the fluid through the that 236 and252, and because as head pressure in the quench tank keeps the pumpsupplied, the fluid will not enter line 240 or valve 238 as theactuating arm 202 engages the valve element of valve 238 upon upwardmovement of the elevator. As the operating fluid enters line 232 andinto the bottom of the cylinder 152, the hydraulic lift is movedupwardly through the quench zone 76 and back into the transfer zone 28.A bleed valve 256 to which a line 258 is connected and that communicateswith the interior of the quench zone isprovided for bleeding thehydraulic system as required.

As previously described, a cooling gas may be introduced into thetransfer zone 28 and circulated therein, and for this purpose a coolingfan 260 is provided that circulates the cooling gas prior to thequenching of heat-treated articles in the quench zone 76. v

It is seen that the system as described herein is completely automatic;and, once the heat-treating cycle has begun with the work cart 72located in the heating zone 30, the operation thereafter is carried outat predetermined intervals, wherein the heat-treated articles are movedinto the transfer zone 28, thereafter moved into the quench zone 76,and, after the quenching operation, are moved upwardly and returned tothe transfer zone 28 for removal from the furnace. By rapidly removingthe articles from the heating zone and quenching in the manner asillustrated and described, the surfaces of the articles beingheat-treated are effectively protected and the desired metallurgicalproperties are attained with minimal distortion of the articles.Protection is further assured by heattreating the articles under vacuumand transferring the articles to the quench zone without removal of thearticle from the vacuum environment. This technique of heating undervacuum and rapidly quenching prevents contamination from occurring onthe surfaces of the articles and further provides the articles with anunusually bright-appearing surface.

It is understood that the vacuum furnace as described herein ispreferably operated to maintain the furnace interior and quench zone ata subatmospheric pressure even during quenching. However it iscontemplated that after evacuating the furnace to remove thecontaminants and impurities therefrom, the heating zone, transfer zoneand the area above the quench liquid can be backfilled with a suitableatmosphere so that the heat-treating and quenching operations arecarried out at partial pressures or even at positive pressures. Thuseven though the heat-treating, cooling and quench cycles could becarried out in positive pressures with respect to atmosphere, thefurnace interior must still be evacuated initially and the unit wouldstill be designated as a vacuum furnace.

While there is shown and described herein certain specific structureembodying the invention, it will be manifest to those skilled in the artthat various modifications and rearrangements of the parts may be madewithout departing from the spirit and scope of the underlying inventiveconcept and that the same is not limited to the particular forms hereinshown and described except insofar as indicated by the scope of theappended claims.

What we claim is:

1. In a vacuum furnace construction for heat-treating metallic articles,a housing having a heating zone and a transfer zone located therein inadjacent relation, means for transferring articles from said heatingzone to said transfer zone after the heating cycle, a quench zonecontaining a quench liquid therein and located below said transfer zonein open communication therewith, an elevator located in said housing formoving said articles from said transfer zone after the heating cycleinto said quench liquid for a predetermined time interval to quench saidarticles and for returning said articles to said transfer zone followingthe quenching thereof, means for reducing the pressure in said housingso that the heating zone, transfer zone and quench tank are maintainedat a subatmospheric pressure during the heating and quenching cycles,and means located within said quench zone for vertically moving saidelevator at the required intervals for carrying out the quenchingoperation and for returning the elevator to the transfer zone.

2. In a vacuum furnace construction as set forth in claim 1, saidheating zone including an insulating cage located therein, a pluralityof heating elements located in said insulating cage, a pivotally mountedinsulating door positioned on said insulating cage and movable to anopen position to expose the interior of said insulating cage formovement of said articles therein, and means located exteriorly of saidhousing and operatively connected to said insulating door for movingsaid door to and from the closed position thereof.

3. In a vacuum furnace construction for heat-treating metallic articles,a housing having a heating zone and a transfer zone located therein inadjacent relation, means for transferring articles from said heatingzone to said transfer zone after the heating cycle, a quench zonecontaining a quench liquid therein and located below said transfer zonein open communication therewith, an elevator located in said housing formoving said articles from said transfer zone after the heating cycleinto said quench liquid for a predetermined time interval to quench saidarticles and for returning said articles to said transfer zone followingthe quenching thereof, means for reducing the pressure in said housingso that the heating zone, transfer zone and quench tank are maintainedat a subatmospheric pressure during the heating and quenching cycles,and means located within said quench zone for vertically moving saidelevator at the required intervals for carrying out the quenchingoperation and for returning the elevator to the transfer zone, the meansfor vertically moving said elevator including a hydraulic lift, theoperating fluid for which is obtained from the quench liquid in saidquench zone.

4. In a vacuum furnace construction as set forth in claim 3, theoperating cylinder of said hydraulic lift being located in said quenchzone and being immersed in said quench liquid.

5. In a vacuum furnace construction as set forth in claim 4, means forcontrolling said hydraulic lift so as to move said elevator and thearticles as received from said heating zone at a relatively slow ratefrom said transfer zone to a point just above the surface of the quenchliquid, at a relatively fast rate through the surface of the quenchliquid and downwardly therein well under said surface and then at arelatively slow rate to a rest position at the bottom of said quenchzone.

6. In a vacuum furnace construction as set forth in claim 5, saidcontrolling means including an actuating member movable with saidelevator and a control valve located exteriorly of said tank forengagement by said actuating member, said control valve being responsiveto engagement by said actuating member upon vertical movement of saidelevator for bleeding fluid from said lift cylinder into said quenchzone for inducing the fast rate of movement of said elevator.

7. In a vacuum furnace construction, a housing having a heating zone anda transfer zone located therein in adjacent relation, a plurality ofrollers mounted in fixed position in said housing in horizontal spacedrelation and extending into said heating zone, a work cart mounted formovement on said rollers, said work cart being defined by a U-shapedframe having parallel legs, each of said legs having a channelconfiguration for receiving said rollers therein and a plurality ofcrossbars interconnecting said legs and for receiving a work basketthereon, a quench tank located in said housing below said transfer zoneand in open communication therewith, and an elevator mounted forvertical movement in said transfer zone and quench tank, said elevatorincluding a plurality of fixed rollers located in aligned relation withrespect to the rollers mounted in said heating zone when said elevatoris positioned in the transfer zone, said elevator rollers receiving saidchannel-shaped legs of said work cart thereon for locating said workcart on said elevator, and means for locking said work cart on saidelevator.

8. In a vacuum furnace construction as set forth in claim 7, means forvertically moving said elevator into said quench tank from said transferzone during the quenching operation, said moving means including ahydraulic lift, the operating fluid for which is obtained from thequench liquid in said quench tank.

9. In a vacuum furnace construction as set forth in claim 7, saidlocking means including means for compensating for the vertical movementof said elevator during the quenching operation to retain the work cartin locked position on said elevator during movement of said elevatorfrom said transfer zone to the quench tank and return to the transferzone.

10. In a vacuum furnace construction for heat-treating metallicarticles, a housing having a heating zone and a transfer zone locatedtherein in adjacent relation, a quench zone located in said housingbelow said transfer zone and in open communication therewith, a workcart for carrying said articles and being movable between said heatingand transfer zones, elevator means on which said work cart is located atthe transfer zone and for moving the work cart into said quench zonefollowing the healing cycle, and means for tethering said work cartduring movement thereof to said heating zone from said transfer zone,said tethering means including means for retracting said work cart fromsaid heating zone to said transfer zone after the heating cycle, saidtethering means further including means for compensating for movement ofsaid work cat in the locked position on said elevator means when saidelevator means is moved to and from the quench tank during the quenchingoperation.

11. In a vacuum furnace construction as set forth in claim 10, saidtethering means including an elongated tape joined to one end of saidwork cart and being received on a reel in wound relation, and meanslocated exteriorly of said housing for rotating said reel for retractingsaid tape thereon when said work cart is moved from the heating zoneonto the elevator means in the transfer zone, and for retaining saidwork cart in locked position on said elevator means.

12; In a vacuum furnace as set forth in claim 11, said compensatingmeans including a vertically movable roller around which said tapeextends and that moves vertically with said elevator means during thequenching operation, wherein said tape is retained in taut relation totether said work cart during vertical movement of said elevator means.

13. In a vacuum furnace as set forth in claim 10, said work cartincluding a bracket secured to an end thereof, said retracting meansfurther including a tape, one end of which is connected to a bar that isreceived in said bracket, wherein operation of said retracting meanscauses said tape to wind and thereby draw said work cart from saidheating zone to a locked position on said elevator means at saidtransfer zone.

2. In a vacuum furnace construction as set forth in claim 1, saidheating zone including an insulating cage located therein, a pluralityof heating elements located in said insulating cage, a pivotally mountedinsulating door positioned on said insulating cage and movable to anopen position to expose the interior of said insulating cage formovement of said articles therein, and means located exteriorly of saidhousing and operatively connected to said insulating door for movingsaid door to and from the closed position thereof.
 3. In a vacuumfurnace construction for heat-treating metallic articles, a housinghaving a heating zone and a transfer zone located therein in adjacentrelation, means for transferring articles from said heating zone to saidtransfer zone after the heating cycle, a quench zone containing a quenchliquid therein and located below said transfer zone in opencommunication therewith, an elevator located in said housing for movingsaid articles from said transfer zone after the heating cycle into saidquench liquid for a predetermined time interval to quench said articlesand for returning said articles to said transfer zone following thequenching thereof, means for reducing the pressure in said housing sothat the heating zone, transfer zone and quench tank are maintained at asubatmospheric pressure during the heating and quenching cycles, andmeans located within said quench zone for vertically moving saidelevator at the required intervals for carrying out the quenchingoperation and for returning the elevator to the transfer zone, the meansfor vertically moving said elevator including a hydraulic lift, theoperating fluid for which is obtained from the quench liquid in saidquench zone.
 4. In a vacuum furnace construction as set forth in claim3, the operating cylinder of said hydraulic lift being located in saidquench zone and being immersed in said quench liquid.
 5. In a vacuumfurnace construction as set forth in claim 4, means for controlling saidhydraulic lift so as to move said elevator and the articles as receivedfrom said heating zone at a relatively slow rate from said transfer zoneto a point just above the surface of the quench liquid, at a relativelyfast rate through the surface of the quench liquid and downwardlytherein well under said surface and then at a relatively slow rate to arest position at the bottom of said quench zone.
 6. In a vacuum furnaceconstruction as set forth in claim 5, said controlling means includingan actuating member movable with said elevator and a control valvelocated exteriorly of said tank for engagement by said actuating member,said control valve being responsive to engagement by said actuatingmember upon vertical movement of said elevator for bleeding fluid fromsaid lift cylinder into said quench zone for inducing the fast rate ofmovement of said elevator.
 7. In a vacuum furnace construction, ahousing having a heAting zone and a transfer zone located therein inadjacent relation, a plurality of rollers mounted in fixed position insaid housing in horizontal spaced relation and extending into saidheating zone, a work cart mounted for movement on said rollers, saidwork cart being defined by a U-shaped frame having parallel legs, eachof said legs having a channel configuration for receiving said rollerstherein and a plurality of crossbars interconnecting said legs and forreceiving a work basket thereon, a quench tank located in said housingbelow said transfer zone and in open communication therewith, and anelevator mounted for vertical movement in said transfer zone and quenchtank, said elevator including a plurality of fixed rollers located inaligned relation with respect to the rollers mounted in said heatingzone when said elevator is positioned in the transfer zone, saidelevator rollers receiving said channel-shaped legs of said work cartthereon for locating said work cart on said elevator, and means forlocking said work cart on said elevator.
 8. In a vacuum furnaceconstruction as set forth in claim 7, means for vertically moving saidelevator into said quench tank from said transfer zone during thequenching operation, said moving means including a hydraulic lift, theoperating fluid for which is obtained from the quench liquid in saidquench tank.
 9. In a vacuum furnace construction as set forth in claim7, said locking means including means for compensating for the verticalmovement of said elevator during the quenching operation to retain thework cart in locked position on said elevator during movement of saidelevator from said transfer zone to the quench tank and return to thetransfer zone.
 10. In a vacuum furnace construction for heat-treatingmetallic articles, a housing having a heating zone and a transfer zonelocated therein in adjacent relation, a quench zone located in saidhousing below said transfer zone and in open communication therewith, awork cart for carrying said articles and being movable between saidheating and transfer zones, elevator means on which said work cart islocated at the transfer zone and for moving the work cart into saidquench zone following the heating cycle, and means for tethering saidwork cart during movement thereof to said heating zone from saidtransfer zone, said tethering means including means for retracting saidwork cart from said heating zone to said transfer zone after the heatingcycle, said tethering means further including means for compensating formovement of said work cart in the locked position on said elevator meanswhen said elevator means is moved to and from the quench tank during thequenching operation.
 11. In a vacuum furnace construction as set forthin claim 10, said tethering means including an elongated tape joined toone end of said work cart and being received on a reel in woundrelation, and means located exteriorly of said housing for rotating saidreel for retracting said tape thereon when said work cart is moved fromthe heating zone onto the elevator means in the transfer zone, and forretaining said work cart in locked position on said elevator means. 12.In a vacuum furnace as set forth in claim 11, said compensating meansincluding a vertically movable roller around which said tape extends andthat moves vertically with said elevator means during the quenchingoperation, wherein said tape is retained in taut relation to tether saidwork cart during vertical movement of said elevator means.
 13. In avacuum furnace as set forth in claim 10, said work cart including abracket secured to an end thereof, said retracting means furtherincluding a tape, one end of which is connected to a bar that isreceived in said bracket, wherein operation of said retracting meanscauses said tape to wind and thereby draw said work cart from saidheating zone to a locked position on said elevator means at saidtransfer zone.